The use of bi-layer resist lift-off processing in the fabrication of integrated circuit components and other thin film structures such as field effect transistors (FET), conductor patterns and magnetic sensing transducers, is well known in the art. For example, U.S. Pat. No. 4,814,258 granted to Tam discloses a bi-layer lift-off process utilized for the fabrication of various types of FETs, and European Patent Application No. 0 341 843 published Nov. 15, 1989 discloses a bi-layer metal lift-off process for forming conductor patterns on a substrate.
Basically, the bi-layer lift-off system comprises a release layer formed on a suitable substrate which is then covered by a top imaging layer of photoresist. A Diazonapthoquinone (DNQ)/Novolac positive resist is suitable for use as the top imaging layer. Polydimethylglutarimide (PMGI), a polymer supplied by the Shipley Company, is a suitable material which is typically used as a release layer. The top imaging layer is exposed and developed to provide the desired pattern. The release layer is then flood exposed and developed to expose the substrate surface for subsequent deposition of the desired structural features. During the development step, the release layer is undercut from the edges of the resist pattern a desired amount to facilitate the subsequent lift-off step.
A major difficulty and limitation of the bi-layer lift-off process utilizing PMGI as the release layer is the loss of, or reduced adhesion of, the PMGI layer to the underlying substrate surface at low prebake temperatures. Good adhesion of PMGI to various substrate materials has been obtained by oven baking at temperatures in the range of 190° to 290° C., near or above the glass transition temperature for the PMGI resin.
However, bake temperatures below 150° C., have resulted in, at best, marginal adhesion characteristics. Further, the relatively high prebake temperatures required for suitable adhesion in PMGI systems can result in oxidation of the underlaying deposition surface, particularly certain metals, further resulting in reduced yields and degraded performance of the finished product.
One solution to this problem is disclosed in Krounbi, et al., U.S. Pat. No. 5,604,073 which teaches enhancing adhesion through addition of azo-type dyes to polydimethylglutarimide. However, this solution still provides results of uncontrolled adhesion failure in some instances and undesirable sublimation of the dye from the film.
The use of patterned photoresist and electroplating, commonly called a plate-through-mask technique, is another method well known the art for the fabrication of integrated circuit components and other thin film structures such as field effect transistors (FET), conductor patterns and magnetic sensing transducers.
For the current generation of write heads in development, high-moment NiFe plating is necessary at P1P and P2 to achieve the targeted magnetic performance. The low temperature and low pH required result in a plating environment with significant stress on the photoresist. As a result of the stress, the photoresist cracks during plating. More particularly, at the highest stress areas, metals press against the walls of the resist structure. The compression against the soft resist causes the resist to deform and crack and/or peel from the surface. The plating solution fills the cracks and if contact is made with the seed layer, NiFe plates in the cracks, forming “fingers” that plate into the cracks. When the resist is removed, the “fingers” of plated metal remain on the substrate in various locations. The unwanted plating adversely affects functionality and reliability of the writer.
As a result, there is a need for compositions and processes which provide films having enhanced adhesion which can also be used in photoresist processes.
There is also a need for compositions and processes which provide films forming a barrier layer that prevents plating into cracks in the resist structure.